A Killer Past — Maris Soule

Seventy-four-year-old Mary Harrington doesn't want to revive her past. She certainly doesn't want her son and granddaughter to know exactly what she was doing forty-four years ago. But when two teenagers from a local gang attempt to mug her, old habits prove hard to forget. Sergeant Jack Rossini--Rivershore, Michigan's lone investigative detective--initially doesn't believe an old woman could have put the youths in the hospital. But once he meets Mary, he becomes curious; and his interest is piqued further when he discovers that there's no record of her existence before moving to Rivershore.